1. Field of the Invention
The present invention relates to method of manufacturing silver halide emulsions and apparatus thereof for producing photographic silver halide emulsions comprising silver halide particles.
2. Description of Related Art
There have been various types of method to form silver halide particles used as photographic photosensitive material.
Those particles are commonly formed by the reaction of silver ions and halide ions in a sufficiently great reactor equipped with a stirrer having a stirring blade or blades. In such a case, efficiency of stirring in the reactor is important, and therefore various types of stirring are proposed as described, for example, in Japanese Patent Application Laid-Open Nos. 7-219092, 8-171156 and 4-283741, Japanese Patent Publication Nos. 8-22739 and 55-10545, and U.S. Pat. No. 3,782,954.
In order to form silver halide particles (for example, particles with a high monodispersity, particles with a high ratio of plates in case of planar particles etc.) preferable as photographic silver halide emulsions, one of the functions required on these stirrers is to mix homogeneously and instantaneously in a microscopic scale. To achieve homogeneous mixing, a method is often adopted of diluting aqueous silver salt solution and aqueous halide salt solution to be added with a liquid already present in the reactor before both salts react with each other. However, the emulsion of silver halide particles thus obtained is commonly not preferable as photographic photosensitive material, unless they are well diluted. For example, in the case where the solutions are added in the phase of nuclear formation to prepare planar particles, a higher ratio of nonparallel cubic twin and a higher polydispersity of planar particles are observed in growing particles, if stirring is not sufficient and/or the solutions have not been diluted well. This phenomenon can be verified by decreasing revolving speed using the stirrer which is described in Japanese Patent Publication No. 55-10545.
Furthermore, in the case where poor dilution occurs in the growing phase, new nuclei form near the inlet for addition and remain as solid without complete dissolution, so that particles formed in the growing phase are incorporated into the emulsion of silver halide particles obtained. Such a phenomenon is observed markedly in the particular case of growth at a high supersaturation.
The above discussion suggests that stirring is important and active use of the bulk solution for dilution may be preferred. However, since the bulk solution usually contains particles already formed, the problem of recirculation then arises wherein particles once formed circulates again near the entering solutions. If recirculation occurs in the phase of nuclear formation, recirculating nuclei prevents formation of new nuclei. Accordingly, in the case where an emulsion of smaller particles is to be prepared, for example, increased addition of the solutions for nuclear formation will not bring about corresponding increase in nuclear formation, indicating that recirculation exerts an adverse effect on formation of smaller particles. In addition, since a difference in particle size arises between nuclei grown by recirculation and those not grown, nuclear polydispersity due to recirculation makes it difficult to prepare an emulsion of monodispersed particles, indicating again that recirculation exerts an adverse effect.
A method of applying microparticles prepared preliminarily to the nuclear formation process or the nuclear growth process is available in order to solve these problems. In this method, aqueous silver salt solution, aqueous halide salt solution, and in many cases, aqueous solution of a dipersing agent as well are introduced into a reaction vessel of small volume, while microparticles are removed through the outlet in parallel and continuously. The microparticles obtained can be used for nuclear formation and/or nuclear growth.
This method has the advantage of achieving more easily increased formation of nuclei due to much less recirculation. It is desirable to minimize the size of produced nuclei in order to maximize the number of nuclei. However, more powerful stirring is required to attain satisfactory mixing because the stirrer used in this method cannot take advantage of the above-mentioned dilution effect caused by the bulk solution. In case of unsatisfactory stirring, for example, for preparing an emulsion of planar particles, increased production of undesirable non-planar particles is one of the problems. In the mixer, as described in Japanese Patent Application Laid-Open No. 6-507255, the ratio of non-planar particles increases, compared to a mixer used in the presence of circulating bulk solution. In addition, in the mixer, as described in Japanese Patent Application Laid-Open No. 8-332364, high speed stirring has difficulty in keeping the perimeter of the rotational axis sealed.
Silver halide microparticles may be also introduced into another reaction vessel containing silver halide seed particles to grow the seed particles. Silver halide microparticles can be formed using the stirrer described in Japanese Patent Application Laid-Open No. 10-43570, or Japanese Patent Application Laid-Open No. 1-183417, and they can be used for growing seed particles.
The stirrer, for example, described in Japanese Patent Application Laid-Open No. 10-43570, as shown in FIG. 3, comprises a stirring container 5 where a given number of inlets 1, 2 and 3 are provided to introduce liquids to be mixed and an outlet 4 is also provided to remove the liquid produced after they are stirred, a pair of stirring blades 6, 6 which are arranged at facing positions spaced apart in the stirring container 5 and driven to rotate in directions opposite to each other so as to control the stirred state of the liquid in the stirring container, and driving means 8, 8 which arrange outer magnets 7, 7 out of the stirring container, the magnets 7, 7 being composed of magnetic couplings which are aligned close to the respective stirring blades 6, 6 out of the walls of the stirring container and without a through axis, and drives the outer magnets 7, 7 rotationally so as to revolve the stirring blades 6, 6.
Use of this method enables uniform mixed crystals or very thin planar particles to be prepared because a highly concentrated area of silver ions or halide ions is unlikely to exist, compared with the method of adding aqueous silver salt solution and aqueous halide salt solution. In this method, silver halide microparticles as source of seed particles are preferably dissolved rapidly, and for the purpose preferably have small diameters and no crystal defects such as twin.
In case of using silver halide microparticles for growing seed particles, aqueous silver salt solution and aqueous halide salt solution preferably have higher concentrations when they are added on formation of silver halide microparticles. However, as the concentrations of the solutions to be added increase, produced microparticles tends to have polydispersity due to no available dilution by the bulk solution, and when the microparticles are transferred into the vessel for growing seed crystals, larger particles or particles containing twin become undissolved to remain. These remaining microparticles interfere with spectral and chemical sensitizations of the emulsion of silver halide particles, and also cause unfavorable light scattering, indicating that such an emulsion of silver halide particles containing remaining microparticles of silver halide is not preferable as photographic photosensitive material.
Accordingly, obtaining an emulsion of silver halide microparticles with small mean size or an emulsion of silver Halide microparticles with monodispersity is important to obtain an emulsion of silver halide particles favorable as photographic photosensitive material.
As another method of forming silver halide particles which is different from the mixing means described above using stirring blades for revolution, a method of manufacturing an emulsion of silver halide microparticles by flowing in line solutions submitted for reaction and applying kinetic energy of the fluids to mixing reaction is disclosed in Japanese Patent Application Laid-Open Nos. 4-139440 and 4-139441, U.S. Pat. No. 5,484,697 and Japanese Patent Application Laid-Open No. 11-217217.
For example, the apparatus described in Japanese Patent Application Laid-Open No. 4-139440, as shown in FIG. 4, is configured so that silver salt solution is introduced through the front end 10A of the nozzle 10, while halide salt solution is introduced through the front end 11A of the nozzle 11, and the resultant silver halide is discharged through the outlet 12. As another example, the apparatus described in Japanese Patent Application Laid-Open No. 4-139441, as shown in FIGS. 5(a) and 5(b), is configured so that a flow of silver salt solution in the nozzle 13 is a counterflow against a flow of halide salt solution in the nozzle 14 at the merging zone 15, and silver halide particles produced there by means of mixing reaction is discharged via the channel 16. Reference characters 13A and 14A denote the front ends of both nozzles.
However, in any method disclosed in these publications, Japanese Patent Application Laid-Open Nos. 4-139440 and 4-139441, U.S. Pat. No. 5,484,697 and Japanese Patent Application Laid-Open No. 11-217217, the concentrations of the solutions undergoing the reaction must be only not more than 0.3 mol/l to achieve formation of microparticles of intended size and prevent agglomeration of the particles, resulting in too low a productivity to produce the particles commercially.
For example, in U.S. Pat. No. 5,484,697, the claims describe that the concentration of silver salt solutions in use ranges from 0.04 to 0.3 mol/l. In Japanese Patent Application Laid-Open Nos. 4-139440, 4-139441 and 11-217217, the concentrations of the solutions used for mixing reaction are not more than 0.5 mol/l in any case.
Furthermore, in the methods disclosed in these publications, at the front ends 10A to 14A where silver salt solution and halide salt solution meets for a moment, agglomerates have deposited in clods and it has been difficult to obtain microparticles with uniform performance steadily. The reason is supposed as follows: on the wall itself of the nozzle tube where the solution flows, the flow rate of the solution is zero, and so a portion of particles produced by the reaction does not flow but deposits gradually on the wall of the nozzle tube to form clods of agglomerates. When the reaction solution flows for a long time in a stationary state where the Reynolds number is not more than 2,100, especially as described in U.S. Pat. No. 5,484,697, this phenomenon of agglomeration becomes remarkable. In addition, as shown in Japanese Patent Application Laid-Open No. 11-217217, even when the Reynolds number is 3,000 or more, the solution flowing at the mean velocity of 5 to 6 m/sec causes agglomeration similar to that described above if the solution has a concentration of 0.1 mol/l or more.
In this way, conventional methods or apparatus of manufacturing silver halide emulsions cannot steadily produce microparticles of mean size not more than 0.3 xcexcm and their commercial production is not feasible.
The present invention has been attained considering this state of the art and eliminated conventional defects. The object of the invention is to present a method of manufacturing silver halide emulsions and apparatus thereof, wherein microparticles for silver halide emulsions which are microscopic, monodisperse and of a low rate of twin formation can be produced with a high productivity, even when the concentration of aqueous silver salt solution in use is 0.3 mol/l or more.
In order to attain the object described above, the present invention is directed to a method of manufacturing a silver halide emulsion, wherein: a jet of aqueous silver salt solution and a jet of aqueous halide salt solution are forced to merge in a merging zone to induce mixing action by means of kinetic energy of fluid in the merging zone; aqueous hydrophilic dispersant solution is then supplied continuously between the two jets which have already merged to mix the three solutions instantaneously; and the mixed solution containing silver halide particles which have been formed by reaction caused by the mixing is immediately removed out of the merging zone.
Further, in order to attain the object described above, the present invention is directed to an apparatus for manufacturing a silver halide emulsion, the apparatus comprising: a mixing reaction pipe comprising: a first tubing through which aqueous silver salt solution flows; a second tubing through which aqueous halide salt solution flows; a third tubing through which aqueous hydrophilic dispersant solution flows; and an exhaust pipe, wherein in a merging zone where outlets of the first and second tubings are merged, an outlet of the third tubing is merged so as to be placed between the outlets of the first and second tubings, the exhaust pipe is provided to discharge out of said merging zone a mixed solution of said three solutions that have merged in said merging zone, and mixing reaction in said merging zone forms silver halide particles; a first jet forming device which forms a jet of the aqueous silver salt solution charged through said first tubing into said merging zone; a second jet forming device which forms a jet of the aqueous halide salt solution charged through said second tubing into said merging zone; and a metering device which meters the aqueous hydrophilic dispersant solution flowing in said third tubing into said merging zone.
According to the invention, aqueous silver salt solution and aqueous halide salt solution are discharged in the form of jet through each outlet of the respective tubings into the merging zone, and therefore silver halide particles produced by reaction do not deposit as agglomerating clods at the front ends where aqueous silver salt solution and aqueous halide salt solution meet. In this case, flow velocity of jets is preferably not less than 100 m/sec. In addition, when two jets of aqueous silver salt solution and aqueous halide salt solution merge, aqueous hydrophilic dispersant solution is continuously supplied between the two jets, resulting in preventing silver halide particles from agglomerating. Particles then produced in the merging zone are removed at once out of the merging zone. As a result, the phenomena of generation of agglomerating clods is difficult to occur even if the silver salt concentration of aqueous silver salt solution and/or the halide salt concentration of aqueous halide salt solution are elevated, and thereby microparticles for silver halide emulsions which are microscopic, monodisperse and of a low rate of twin formation can be produced in a high concentration range of aqueous silver salt solution and aqueous halide salt solution.